1. Field of the Invention
This invention relates to bone fixation systems which use wire or cable to lock two or more bone segments together, including the back, or spinous process of adjacent vertebrae together or locking a spinal bone to another fixation device. More particularly, the invention relates to a ferrule for protecting the bone from being cut by the cable.
2. Description of the Related Art
In spinal surgery, the surgeon often locks adjacent vertebrae together. In some cases, the surgeon additionally locks adjacent vertebrae together through the spinous process by a cable around bony edges or through holes drilled in the bone.
Stahurski, U.S. Pat. No. 5,304,178, shows a sublaminar wire for connecting a corrective device to the spinal column. A center portion is positionable under the lamina of a vertebra and has a varying cross-sectional area. The inventor notes that wire may tear through the lamina due to their small diameters. Howland, U.S. Pat. No. 5,030,220, discloses a spinal fixation system having pedicle screws and rods as well as sublaminar wires with a wire protector to protect the rod/wire interface. The wires are passed under the lamina and over the wire protectors which encase the serrated rod.
Klein, U.S. Pat. No. 4,590,929, describes the use of twisted wire connections for connecting bone fragments. He notes that apertures in the bone may cause breakage of the wires and reduces wire breakage by cutting the bone at the breakage point.
Johnson et al., U.S. Pat. No. 4,146,022, discloses a method for fixing bone fractures by wire using an implant embedded in the cortex of a bone. The implant has a cylindrical body portion and a circular bore through which a wire may be passed. That device uses spikes into the bone to provide a raised member that prevents the wire from cutting into the bone.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is "prior art" with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. .sctn. 1.56(a) exists.